1. Field of the Invention
The present invention relates to a method of forming a photosensitive film consisting of a specific resin composition prepared by modifying a conjugated diene polymer or copolymer.
More specifically, the present invention relates to a method of manufacturing a printed circuit board using a photosensitive resin film containing a specific resin composition prepared by modifying a conjugated diene polymer or copolymer.
2. Description of the Prior Art
Although various printed circuit board manufacturing methods have been developed, a method using a photosetting resin as an etching resist or plating resist has been mainly used in recent years.
In the former method, a film consisting of a photosensitive resin composition is formed on a copper-clad substrate, and a negative circuit pattern mask is brought into tight contact with the resin film. Active light is then radiated to set a necessary portion of the photosensitive film, a non-set portion (an uncured portion) is removed by development, and etching is performed to obtain a predetermined circuit pattern.
In the latter method, a mask of a reverse pattern is used to remove a resin film on a necessary portion, and this portion is plated by solder as an etching-resistant protecting metal. A resin film on an unnecessary portion is removed, and etching is performed to obtain a predetermined circuit pattern
In this case, the circuit pattern mask. corresponds to a negative of a photograph and is obtained by forming a light-shielding layer defining an arbitrary pattern on a transparent substrate. The substrate sometimes consists of glass but is mainly a plastic film of polyester or the like. A material of the light-shielding layer is a Cr-crosslinked organic film.
Conventionally, an acrylic resin composition is normally used as the photosensitive resin. The acrylic resin normally consists of, e.g., (1) a binder polymer, (2) a photopolymerizable monomer, (3) a photopolymerization initiator, and (4) other additives (a stabilizer, a colorant, and a flame-retarder).
The binder polymer is used to obtain a film-like shape and is mostly an acrylic resin. A molecular weight of the binder polymer is normally several tens of thousands. A monomer having an acryloyl group or methacryloyl group is used as the photopolymerizable monomer. These components are set or cross-linked and insolubilized upon exposure to active light.
A method of using a photosensitive resin composition using maleinized modified oil as a so-called photoresist such as an etching resist is described in, e.g., U.S. Pat. No. 3,954,587. However, the present inventors have found by a tack-free test that this composition is tacky at room temperature before exposure to light since a mixture of maleinized modified oil and a liquid ethylenic unsaturated compound having two or more unsaturated bonds in one molecule is used.
In order to manufacture a printed circuit board, a circuit pattern mask is normally vacuum-chucked to a formed photosensitive film and UV-exposed. If the photosensitive film is tacky, the film partially adheres on the circuit pattern mask, and the mask may be injured when it is removed. In order to prevent this, a cooling unit or cooling trough may be equipped with after the exposure unit. This is not preferable, however, since an installation cost is increased, and the number of manufacturing steps is also increased to result in a cumbersome operation. It is also undesirable to coat a releasant (a releasing agent) on a circuit pattern mask or a photosensitive resin film in terms of exposure properties. In addition, labor and the manufacturing cost are increased.